What are descriptive and inferential statistics?

Descriptive and inferential statistics are the two main branches of the science of statistics.

Descriptive statistics

Descriptive statistics provide a concise summary of data. You can summarize data numerically or graphically. For example, the manager of a fast food restaurant tracks the wait times for customers during the lunch hour for a week and summarizes the data.

The manager calculates the following numeric descriptive statistics:
Statistic Sample value
Mean 6.2 minutes
Standard deviation 1.5 minutes
Range 3 to 10 minutes
N (sample size) 50
The manager examines the following graphs to visualize the wait times:
Histogram of wait times
Boxplot of wait times

Inferential statistics

Inferential statistics use a random sample of data taken from a population to describe and make inferences about the population. Inferential statistics are valuable when it is not convenient or possible to examine each member of an entire population. For example, it is impractical to measure the diameter of each nail that is manufactured in a mill, but you can measure the diameters of a representative random sample of nails and use that information to make generalizations about the diameters of all the nails produced.